1. Field of the Invention
The present invention relates to an information-processing apparatus comprising a plurality of processing units operable to perform respectively predetermined process, respectively, and a memory unit. The information-processing apparatus and the memory unit being operable as an externally accessible memory device when operation mode is switched.
2. Description of the Related Art
In recent years, infrastructures of high-speed telecommunication including third generation mobile communications have been widely prepared, with a remarkable increase in the amount of information that can be transmitted. Consequently, data that is transmitted in the mobile communications may contain not only data of audio, text and still images, but also data of moving pictures.
MPEG-4, which is proposed by the Moving Picture Experts Group, is adapted as a moving picture-coding format in the third generation mobile communications. Generally, when moving pictures are processed according to MPEG-4, huge amount of processes are needed. When a mobile telecom terminal, which is driven by a battery, adopts MPEG-4, problems encountered by the mobile telecom terminal include a need for rapid processing of the huge amount of data, and lowering power consumption.
From this viewpoint, a moving picture-processing-designed LSI, which is mounted in the mobile telecom terminal, comprises a processor and a plurality of special purpose hardware, thereby, distributing load in processing moving pictures, as well as reducing power consumption.
Assume that the moving picture-processing-designed LSI is implemented onto an image-processing apparatus. When the image-processing apparatus processes a still image, the moving picture-processing-designed LSI does not operate in many cases. Meanwhile, the plurality of special purpose hardware of the moving picture-processing-designed LSI, contain respective local memories.
In order to effectively use resources of the image-processing apparatus, it is considerable to utilize for other purposes the local memories of the moving picture-processing-designed LSI, when the moving picture-processing-designed LSI does not operate. It is further considerable to change an operation mode of the moving picture-processing-designed LSI to make the local memories of the moving picture-processing-designed LSI accessible externally.
A document 1 (Japanese Patent Application Laid-Open No. H07-78876) discloses conventional arts to change a mode to make a plurality of circuit blocks externally accessible.
FIG. 9 is a block diagram of a conventional LSI 900 that enables external access to the plurality of circuit blocks. FIG. 9 corresponds to FIG. 1 of the document 1. The LSI 900 comprises a mode decoder 902, an I/O selector 903, a first circuit block 901a, a second circuit block 901b, and a third circuit block 901c. Based on mode setting data supplied from the outside, the I/O selector 903 selects one of the first circuit block 901a, the second circuit block 901b, and the 3rd circuit block 901c. The mode decoder 902 changes an operation mode of the selected circuit block, and data is transmitted between the selected circuit block and the outside via a terminal 904.
However, if the above-mentioned art is improved such that local memories contained by the circuit blocks can be accessed from the outside, amount of data that can be transmitted at once is limited to the capacity of a local memory of one circuit block. Furthermore, whenever a circuit block to which a local memory to be used belongs is changed, operation modes of two corresponding circuit blocks (a current circuit block and a next circuit block) should be changed. Therefore, complicated processes cannot be avoided.
Values of capacity, bit width and address width of the local memories are optimized according to functions of the circuit blocks to which the local memories belong, respectively. In general, the values are different for every circuit block. A programmer or a designer, who utilizes the local memories from the outside, should take into consideration the values of capacity, bit width and address width of each local memory.
In some cases, the local memories are composed of different kinds of memories (an SRAM and a DRAM, and so on), all of the local memories cannot be accessed using one kind of memory-accessing method. In other words, a plurality of memory-accessing methods should be prepared, and a method suitable for current accessing should be selected to use among the plurality of memory-accessing methods, therefore, handling the local memories is troublesome.